The objectives of this proposal are (1) a genetic analysis of meiotic mutants which act in male Drosophila melanogaster, (2) an analysis of the disjunctional patterns of Y-2 translocations and the use of these translocations to identify the regions of the chromosome that are necessary for chromosome pairing, and (3) an analysis of the disjunction patterns of compound autosomes. Three meiotic mutants are available for analysis. One mutant is chromosome specific and acts in both sexes. Experiments have been designed to determine at which division the mutant acts and whether the specificity is due to the centromere. The second mutant may permit nonhomologous pairing to occur. Experiments have been designed to explore its behavior with respect to nondisjunction of two or more pairs of chromosomes. Analysis of the third mutant has just begun. Preliminary investigations with Y-autosome translocations indicate that the centromere plays an important role in determining chromosome orientation for disjunction. Additional studies will determine whether the centromere is also the primary site of chromosome pairing, or whether other regions of the chromosome are important in chromosome synapsis. An investigation of two compound-2 stocks has shown that in males, compound segregation is not always random. It is postulated that the nonrandom segregation is due to differences in the heterochromatin. New compound chromosomes will be synthesized such that the amount of missing and/or extra heterochromatin will be known, and these chromosomes will be analyzed for their segregational behavior. The genetic control of meiosis is different in male and female Drosophila, and the objective of this proposal is to provide a picture of the meiotic system in males, which has not been studied in any detail. An understanding of both systems will provide the necessary background for further investigations into the mechanisms and regulation of these two systems.